/*
* $Header$
* $Revision: 982 $
* $Date: 2006-12-08 18:42:51 +1000 (Fri, 08 Dec 2006) $
*
* ====================================================================
*
* The Apache Software License, Version 1.1
*
* Copyright (c) 2003-2009 The JRDF Project. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
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* 1. Redistributions of source code must retain the above copyright
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* 2. Redistributions in binary form must reproduce the above copyright
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* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowlegement:
* "This product includes software developed by the
* the JRDF Project (http://jrdf.sf.net/)."
* Alternately, this acknowlegement may appear in the software itself,
* if and wherever such third-party acknowlegements normally appear.
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* 4. The names "The JRDF Project" and "JRDF" must not be used to endorse
* or promote products derived from this software without prior written
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* 5. Products derived from this software may not be called "JRDF"
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* ====================================================================
*
* This software consists of voluntary contributions made by many
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* information on JRDF, please see <http://jrdf.sourceforge.net/>.
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package org.jrdf.query.relation.operation.mem.union;
import org.jrdf.query.relation.EvaluatedRelation;
import org.jrdf.query.relation.Tuple;
import org.jrdf.query.relation.operation.Union;
import org.jrdf.query.relation.operation.mem.common.RelationProcessor;
import org.jrdf.query.relation.operation.mem.join.TupleEngine;
import java.util.LinkedHashSet;
/**
* Minimum union is a combination of outer union and tuple subsumption. It is similar to the relational
* union operation except that the types of the two relations do not need to match and rows that contain
* less values bound than another row (more nulls than another row or are subsumed by) are removed.
*/
public class MinimumUnionImpl implements Union {
private RelationProcessor relationProcessor;
private TupleEngine unionTupleEngine;
private TupleEngine subsumptionTupleEngine;
public MinimumUnionImpl(RelationProcessor newRelationProcessor, TupleEngine newUnionTupleEngine,
TupleEngine newSubsumptionTupleEngine) {
this.relationProcessor = newRelationProcessor;
this.unionTupleEngine = newUnionTupleEngine;
this.subsumptionTupleEngine = newSubsumptionTupleEngine;
}
public EvaluatedRelation union(EvaluatedRelation relation1, EvaluatedRelation relation2) {
UnionSimplification unionSimplification = new UnionSimplificationImpl();
LinkedHashSet<EvaluatedRelation> relations = unionSimplification.simplify(relation1, relation2);
if (relations.size() == 1) {
return relations.iterator().next();
} else {
return performMinimumUnion(relations);
}
}
private EvaluatedRelation performMinimumUnion(LinkedHashSet<EvaluatedRelation> relations) {
EvaluatedRelation relation = relationProcessor.processRelations(relations, unionTupleEngine);
EvaluatedRelation subsumptionRelation = relationProcessor.processRelations(relations, subsumptionTupleEngine);
for (Tuple tuple : subsumptionRelation.getTuples()) {
relation.getTuples().remove(tuple);
}
return relation;
}
}